Air fuel injector and control

ABSTRACT

A fuel/air injector for a crankcase compression two-cycle internal combustion engine and control strategy therefore wherein under a first load range of the engine which is generally a low speed, low load range, fuel is supplied to the fuel/air injector at a time which does not precede the opening of the injector valve and then as the load and speed of the engine increase, the timing of opening of the injector valve is advanced until a certain condition is reached and thereafter the opening of the injector valve is held constant and the timing of fuel supply is advanced so that fuel supply precedes the opening of the injector valve.

BACKGROUND OF THE INVENTION

This invention relates to an air/fuel injector and control for aninternal combustion engine.

In order to improve the performance of an internal combustion engine andparticularly its fuel economy and exhaust emission control, it has beenproposed to employ direct cylinder fuel injection. It has further beenproposed to improve the atomization or disbursement of the fuel supplyto the combustion chamber by the injector by also injecting highpressure air along with the fuel. The types of fuel air injectors whichhave been proposed employ a chamber or a plurality of chambers to whichair and fuel are supplied under pressure and which are delivered to thecombustion chamber when the injector valve is opened. In one form ofcontrol strategy, the fuel is all supplied to its respective chamberbefore the injector valve is opened. In another form of strategy, thefuel is supplied to the chamber during the time when the injector valveis opened. These types of charging strategies, however, present certaindifficulties.

With the precharged type of injector, not all of the fuel may bedischarged from its chamber when the injector valve is opened. Thisresults in poor combustion and uneven combustion. The non-prechargedtype of fuel/air injector, on the other hand, does not present thisproblem but with this type of injector as well as the precharged type,it may be difficult to supply all of the required fuel to the combustionchamber without other problems.

For example, when running at high speed and high load conditions, asubstantial amount of fuel is required. If this fuel must all be chargedinto the chamber of the fuel injector and then into the combustionchamber during the time when the injector valve is opened, it may not bepossible to supply sufficient fuel or, alternatively, the amount of fuelsupplied may be so great that full evacuation of the injector chamberand disbursement of the fuel is not possible. In addition, the durationof opening of the injector valve becomes so great that bouncing of thevalve can be a problem.

A bouncing condition results when the injector valve is closed. Therapid closure of the injector valve tends to cause the valve to againbounce open until its motion is fully dampened and thus additional fuelmay be delivered to the combustion chamber of the engine after the valveis closed. When this occurs, the fuel may actually be delivered at thetime the spark plug is fired and this can give rise to misfiring,pre-ignition and other problems.

The problems aforedescribed are particularly acute in conjunction withtwo cycle crankcase compression engines. With such engines, as is wellknown, there is a substantial overlap between the closing of the exhaustport and the opening of the scavenge port and if the duration of fuelinjection is too long, fuel may be discharged directly out of theexhaust port resulting in poor fuel economy and high exhaust gasemissions, particularly with unburned hydrocarbons.

It is, therefore, a principal object of this invention to provide animproved fuel injector and control for an internal combustion enginewherein adequate amounts of fuel can be delivered to the combustionchamber and fully disbursed without the fear of unburned fuel beingdischarged from the exhaust port of the engine. It is a further objectof this invention to provide an improved air/fuel injector and controltherefore wherein adequate amounts of fuel can be supplied to the engineunder all running conditions without causing pre-ignition or othercombustion difficulties.

It is a further object of this invention to provide an air/fuel injectorand control for an engine wherein the dynamic range of operation of thefuel injector and the operation through this range is significantlyimproved.

SUMMARY OF THE INVENTION

This invention is adapted to be embodied in a fuel/air injector unit andcontrol therefore wherein the injector unit comprises an outer housingassembly that defines chamber means. Air means supply air under pressureto the chamber means and fuel means supply fuel to the chamber means. Aninjector port communicates the chamber means with an engine chamber andan injector valve opens and closes the injector port. Means are providedfor selectively opening and closing the injector port and control meanscontrol the initiation of fuel delivery by the fuel means and the meansfor operating the injector valve.

In a fuel/air injector constructed in accordance with an embodiment ofthe invention the control means initiates fuel delivery by the fuelmeans to the chamber means beginning at a time before the injector valveis opened and terminating after the time the injector valve is openedunder at least one running condition of the engine.

In accordance with a method of operating a fuel injector unit asdescribed, the fuel means is operated to initiate the supply of fuel tothe chamber means before the injector valve is opened and fuel supply isterminated at a time after the injector valve is opened under at leastone running condition of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view taken through a single cylinder of amultiple cylinder internal combustion engine constructed in accordancewith an embodiment of the invention.

FIG. 2 is an enlarged cross sectional view taken through the fuel airinjector of an embodiment of the invention.

FIG. 3 is a graphical timing view showing how the fuel and air aresupplied to the fuel air injector of a prior art type of constructionunder low load, low speed conditions.

FIG. 4 is a timing chart, and similar to FIG. 3, and shows the way thefuel and air is supplied to a prior art type of construction under highspeed, high load conditions.

FIG. 5 is a graphical timing chart showing the fuel/air control inaccordance with an embodiment of the invention under low speedconditions.

FIG. 6 is a graphical view showing the timing chart of the fuel/airinjection in accordance with an embodiment of the invention under highspeed, high load conditions.

FIG. 7 is a graphical view of a timing chart showing how the fuel/aircontrol is varied in accordance with embodiments of the invention.

FIG. 8 is a timing chart showing the fuel/air control under high speed,high load conditions in accordance with the invention.

FIG. 9 is a family of curves of torque and engine speed showing theconditions under which the fuel/air control is varied in accordance withan embodiment of the invention.

FIG. 10 is a graphical view showing the fuel injection valve timingevents in response to varying engine load conditions.

FIG. 11 is a graphical view, in part similar to FIG. 9, showing anotherembodiment of the invention wherein a sub-fuel injector may also beemployed.

FIG. 12 is a graphical view, in part similar to FIG. 10, showing thetiming events when the sub-fuel injector is employed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring first to FIG. 1, a two-cycle crankcase compression internalcombustion engine constructed and operated in accordance with anembodiment of the invention is identified generally by the referencenumeral 21. FIG. 1 is a cross sectional view taken through a singlecylinder of a multiple cylinder engine. It is believed that thoseskilled in the art can readily understand how the invention is practicedwith multiple cylinder engines by a description of a single cylinder ofthe engine. Also, the invention is described in conjunction with areciprocating type of engine, it should be understood that the inventionmay be practiced with other types of engines such as rotary engines.Furthermore, although the invention has particular utility in two-cycleengines, it may also be employed in four-cycle engines. Because of theport timing overlap with two-cycle engines, however, the invention hasgreater utility in such engines.

The engine 21 is comprised of a cylinder block 22 in which a cylinderbore 23 is formed by a liner 24. A piston 25 reciprocates within thecylinder bore 23 and is connected to the upper or small end of aconnecting rod 26 by means of a piston pin 27. The lower end of theconnecting rod 26 is journaled on a throw 28 of a crankshaft 29. Thecrankshaft 29 is rotatably journaled, in a suitable manner, in acrankcase chamber 31 formed by the lower portion of the cylinder block22 and a crankcase member 32 that is affixed to the cylinder block 22 ina known manner. As is typical in two-cycle engine practice, thecrankcase chamber 31 associated with each piston 25 of the engine issealed suitably from the other crankcase chambers of the engine.

An intake charge, which may be either pure air or an air/fuel charge,under some circumstances as will be described, is delivered to thecrankcase chamber 31 through an intake port 33. A reed type check valve34 is positioned in the intake port 33 for precluding reverse flow whenthe piston 25 moves downwardly to compress the charge in the crankcasechamber 31. An air manifold 35 which incorporates an air inlet andsilencing device and throttle valve (not shown) communicates with theintake ports 33.

A combustion chamber 36 is formed above the head of the piston 25 by thepiston head, cylinder bore 23 and a cavity 37 of a cylinder headassembly 38. The cylinder head assembly 38 is affixed to the cylinderblock 22 in a known manner.

The charge which has been compressed within the crankcase chamber 31during downward movement of the piston 25 is transferred to thecombustion chamber 36 through a plurality of scavenge passages 39 whichare formed in the cylinder block 22 and which extend from the crankcasechamber 31 to scavenged port openings 41 formed in the cylinder liner24. This charge is then further compressed in the combustion chamber 36as the piston 25 moves upwardly.

A fuel/air charge is sprayed into the combustion chamber 36 by afuel/air injector assembly, indicated generally by the reference numeral42 and the construction of which will be described in more detail laterby reference to FIG. 2. This fuel/air charge is then fired by means of aspark plug 43 that has its spark gap 44 disposed within the combustionchamber 36. The fuel/air injector 42 and spark plug 43 are controlled byan ECU 45 in accordance with a strategy which will be described. The ECU45 receives input signals a indicative of varying engine conditions suchas air flow through the induction system, pressure in the crankcasechamber 31, engine temperature, throttle valve opening, and any of avariety of other factors including ambient conditions.

The charge which has been fired in the combustion chamber 36 will expandand drive the piston 25 downwardly. The burnt charge is then exhaustedthrough an exhaust passage 46 formed in the cylinder block 22 and whichextends from an exhaust port 47 that is formed in confrontingrelationship to at least one of the scavenge passages 39. An exhaustmanifold (not shown) receives exhaust gases from the exhaust ports 46and delivers them to the atmosphere. If desired, an exhaust controlvalve 48 may be positioned in the exhaust port 47 for controlling eitherthe timing of the opening of the exhaust port 47 and/or the compressionratio. The exhaust control valve 48 may also be controlled by the ECU 45in accordance with any desired strategy.

Referring now in detail to FIG. 2, the air/fuel injector 42 is comprisedof an outer housing assembly 49 made up of primarily a lower housingpiece 51 and an upper housing piece 52 which are connected to each otherin a manner to be described. The lower housing piece 51 has acylindrical pilot portion 53 that is adapted to be inserted into asuitable bore in the cylinder head 38 and affixed thereto in a suitablemanner. A nozzle port 54 is formed at the lower end of the pilot portion53 and terminates in a valve seat 55. An injection valve member,indicated generally by the reference numeral 56 has a head portion 57that cooperates with the valve seat 55 to selectively open and close thenozzle port 54 for communication with the combustion chamber.

The nozzle port 54 terminates at its upper end in a counter bore 58formed in the lower piece 51. An insert 59 is received within the bore58 and defines a first chamber 61 around the outer periphery of theinsert piece 59. The chamber 61 is a fuel chamber and is adapted toreceive fuel that is sprayed by a fuel injector 62 that is mountedwithin a recess 63 of the upper housing piece 52. A seal 64 is formed atthe lower end of this recess 63 and provides a seal around the lower endof this injector 62. The fuel injector 62, when actuated, sprays fuelthrough a fuel delivery port 65 formed in the upper housing piece 52 andwhich communicates with a further fuel delivery port 66 in the lowerhousing piece 51 which, in turn, communicates with the fuel chamber 61.

The insert 59 is formed with an internal bore 67 through which a stem 68of the injector valve 56 passes. This forms a further chamber to whichcompressed air is delivered by a manifold 69 which, in turn,communicates with an air compressor (not shown). The manifold 69 hasdelivery ports 71 that communicate with delivery ports 72 formed in theupper housing piece 52 and which, in turn, communicate with the chamberformed by the bore 67 through passageways formed in an insert sleeve 73which is held in place by a set screw 74.

The injector valve 56 has a plurality of projections 75 which engage thenozzle port 54 so as to provide sliding support for the injector valve56 while, at the same time, permitting flow therepast. The fuel chamber61 communicates with the chamber formed by the insert bore 67 through aplurality of radially extending fuel delivery passages 76.

The area between the chamber formed by the bore 67 of the insert 59 andthe fuel chamber 66 is isolated from the area between the valve head 57and valve seat 55 by means of an orifice, indicated generally by thereference numeral 77 which is formed by an enlargement 78 of the valvestem 68 and a restriction 79 formed at the lower end of the insert piece56. This orifice 77 tends to isolate the aforenoted chambers from thepressure in the combustion chamber so as to provide better fuel/airinjection control.

The lower housing piece 51 is formed within an enlarged cylindricalportion 81 that is received within a bore 82 formed at the lower end ofthe upper housing piece 52. A plurality of socket headed screws 83 fixthe lower and upper pieces 51 and 52 together.

The upper end of the injector valve stem 68 has a threaded portion 84onto which is fixed an armature 85. The armature 85 is held in place bya locknut 86. The armature 85 cooperates with a solenoid winding 87which is energized in response to a signal from the ECU 45 so as to drawthe armature 85 downwardly against the action of a coil spring 88 andopen the injector valve 56 so that the head 57 moves away from the valveseat 55 and fuel and air can be delivered into the combustion chamber.When the solenoid 87 is deenergized, the coil spring 88 will urge theinjector 56 back to its closed position.

A diaphragm 89 is affixed between the locknut 86 and the armature 85 andprovides a seal for the upper housing assembly through cooperation witha cap 91 so as to define a solenoid chamber 92 in which the armature 85and solenoid winding 73 are contained.

Fuel is supplied to the fuel injector 62 by a suitable manner and thefuel injector 62 is, in the illustrated embodiment, of the electricallyoperated type. Referring again to FIG. 1, the ECU puts out a solenoidcontrol signal b that selectively energizes the solenoid winding 73 foropening the injector valve 56 and a fuel control signal c to the fuelinjector 62 so as to control the timing and duration of fuel injection.

In accordance with a type of previously proposed control strategy,called a pre-charged type, fuel is injected by the injector 62 into thefuel chamber 61 during the time period when the injector valve 56 isclosed. FIGS. 3 and 4 are timing curves of this type of prior artconstruction showing low speed, low load and high speed, high loadconditions, respectively. In these curves the timing events of theopening and closing of the exhaust port 47 and the opening and closingof the scavenge ports 41 is depicted in relation to top and bottom deadcenter as is the time of ignition caused by firing of the spark plug 43.

As may be seen in FIG. 3, under low load, low speed conditions, the fuelinjector 62 is operated by commencing injection at some time after theclosing of the exhaust port and concluding it before the injector 56 isopened. The injector valve 56 is then opened and closed for a timeperiod which precedes the timing of firing of the spark plug 49.

Under high speed, high load conditions, the timing of fuel injection byoperation of the injector 62 is advanced and extended so that fuelinjection begins at some point time after the exhaust port closes fromthe previous cycle and before ignition has occurred. The timing of fuelinjection is stopped at approximately the same time when the injectorvalve 66 is opened, at some time after the scavenge ports 41 open.Injection continues until some time after the scavenge port closes asshown in FIG. 4. The problem with this type of construction, however, isthat the bouncing of the injector valve 56, which is almost inherent inthese constructions, causes continuing injection of fuel and air evenafter the valve is initially closed by denergization of the solenoid 73so that some fuel will be injected before the exhaust port closes andpoor fuel economy and high emission hydrocarbons can result. Inaddition, it is difficult to provide full fuel charging and also insurethat all of the fuel will be discharged from the fuel injector underthese conditions.

In accordance with the invention, therefore, a control strategy isemployed, as will be described in conjunction with FIGS. 5 through 8,wherein under low speed, low load conditions, fuel is injected by theinjector 62 at the time when the injector valve 56 is opened. As theload and speed on the engine increase, the timing of opening of theinjector valve 56 is advanced until a fixed point of advance is reachedand then under further increasing loads, the timing of opening of theinjector valve 56 is held constant and the timing of beginning of fuelinjection by the fuel injector 62 is continued to advance. In this way,there is some pre-charging but the main portion of the fuel is stilldelivered when the injector valve 56 is opened so that it will beinsured that all of the fuel will be discharged from the injector valvehousing 49 and specifically the chamber 61 and the chamber formed by theinsert piece bore 67 during each cycle.

Referring first to FIG. 5, the solid curves of this timing diagram showthe operation under low speed, low load. It will be seen that thefuel/air injector valve 56 is opened at a timed duration which is equalto the time duration of injection of fuel from the fuel injector 62.Hence, this timing relationship is of the conventional non pre-chargedtype. It should be noted that the timing of fuel injection by theinjector 62 and opening and closing of the injector valve 56 need not becoincident. For example, the injector valve 56 may be opened slightlybefore fuel injection is commenced from the injector 62 and closed atthe same time fuel injection is terminated as indicated by the solidcurve a or, alternatively, the injector valve 56 may be opened beforefuel injection by the injector 62 is started and closed after fuelinjection by the injector 62 is stopped as shown by the curve b.

As the engine speed and load increases during this low speed first phaseof operation, the timing of opening of the injection valve 56 isadvanced as is the timing of injection of fuel from the injector 62 soas to maintain the same relationship as afore described wherein fuelinjection and opening of the injector valve 62 are substantiallycoincident (FIG. 7). This condition is maintained up through themid-range performance of the engine (FIG. 6). That is mid-range load andspeed conditions. However, at a given point on the curve of load andspeed, as will be described by reference to FIGS. 9 and 10, the timingof the advance of the opening of the injector valve 56 is stopped. Thenas the load of the engine increases, further fuel is supplied bybeginning to inject fuel from the injector 62 before the injector valve56 is opened. This condition is shown in FIG. 6 by the broken line viewand in FIG. 8. It will be noted that the injector valve 56 may be openedinitially at a point in time just slightly before the scavenge port isopened but always after the time when the exhaust port is opened. In apreferred embodiment, the amount of fuel injected into the fuel cavity61 of the fuel/air injector 42 before the injector valve 56 is openednever exceeds 36 per cent of the total amount of fuel required. That is,the majority of the fuel is still injected during the time when theinjector valve 56 is opened. This will insure good purging of the fuelfrom the injector 46 during each cycle of its injection.

Referring now to FIGS. 9 and 10 and initially to FIG. 9, this is afamily of curves showing the torque curve at wide open throttle undervarying load conditions. The portion of the curve under the shadedportion indicated as the area 1 is the first running condition of theengine and the time when no fuel is injected by the injector 62 beforethe injector valve 56 is opened. The shaded line portion of the curveshown by the area 2 is the second running condition, that is the timewhen fuel injection by the injector 62 is advanced so that fuel will beinjected before the fuel injector 56 is opened.

FIG. 10 is a graphical view showing the timing of engine load versusvalve opening duration in terms of crank angle. During the first runningcondition up till the vertical line l₁, the fuel and air injection isadvanced both in timing and duration but the fuel injection never occursbefore the injector valve 56 is opened. However, when the second runningcondition is reached, the injector valve opening is held at a fixedcrank angle and the fuel injection valve opening is advanced until fullload conditions are reached.

It will be noted that because of the described relationship if anybouncing of the injector valve occurs, this bouncing will not cause anyadditional fuel to be delivered to the combustion chamber since all ofthe fuel will have been depleted from the fuel and air injector 42 bythe time the injector valve 56 is closed. As a result, the bouncing willhave no detrimental effect on combustion such as causing misfiring,pre-ignition or the like as with the prior art constructions.

With the strategies as thus far described it will be apparent that theefficiency of the fuel/air injector is good under all running conditionsand also the detrimental effects of the prior art type of constructionsare avoided. However, with this control strategy there may be a timewhen the fuel requirements of the engine are such that they cannot befully supplied by the afore described strategy wherein it is desired toinsure that too much fuel is not injected by the injector 62 into theinjection chamber 61 before the injector valve 56 is opened. To overcomethese problems, a sub or auxiliary fuel injector may be employed forsupplying the additional fuel under these extreme conditions. The sub orauxiliary fuel injector may inject fuel either into the intake manifold35, the crankcase chambers 31, scavenge passages 39 or combustionchamber 36 directly. This sub or auxiliary injector may be either a purefuel injector or a fuel/air injector. If the fuel is injected into thecrankcase chamber 31 or upstream of it, it will provide added coolingunder these high load conditions.

FIGS. 11 and 12 show such an embodiment. FIGS. 11 and 12 correspond toFIGS. 9 and 10 and show the range when no fuel is injected by thesub-injector and when fuel is injected by the sub-injector. It should benoted that the strategy as described causes the fuel injector valve 56to open before the fuel injector 62 is energized during the firstrunning condition and then the timing of the main injection valveopening is held constant and at a given point in time the fuel injector62 will begin to inject fuel before the main injection valve 56 isopened. However, at the time when the sub-injector begins to injectfuel, the beginning of injection by the fuel injector 62 may be retardedslightly and then held constant with the additional fuel requirementsbeing provided solely by the auxiliary or sub-fuel injector.

It should be readily apparent from the foregoing description that thedescribed embodiments are very effective in providing good dynamic rangeof operation of the air/fuel injector, good fuel atomization and goodfuel disbursement without causing problems of misfiring or pre-ignitioneven in the extreme event when the injector valve 56 may bounce. Itshould also be readily apparent that the foregoing description is thatof preferred embodiments of the invention and various changes andmodifications may be made without departing from the spirit and scope ofthe invention, as defined by the appended claims.

We claim:
 1. A fuel/air injector unit comprising an outer housingassembly defining chamber means, air means for supplying air underpressure to said chamber means, fuel means for supplying fuel to saidchamber means, an injector port communicating said chamber means with anengine chamber, an injector valve for opening and closing said injectorport, sensor means for sensing engine running conditions and controlmeans for controlling fuel delivery by said fuel means to said chambermeans and opening and closing of said injector valve in response tosensed engine conditions for varying at least the opening of saidinjector valve at certain sensed engine conditions, holding the time ofopening of said injector valve constant in at least a range of sensedconditions, varying at least the initiation of fuel delivery by saidfuel means at certain sensed running conditions, and initiating the fueldelivery of said fuel means beginning at a time before said injectorvalve is opened and terminating at a time after said injector valve isopened under at least one running condition of said engine.
 2. Afuel/air injector as set forth in claim 1 wherein the duration of fuelinjection is increased as the load of the engine increases during theone running condition of the engine.
 3. A fuel/air injector as set forthin claim 1 wherein there is a second running condition of the enginewherein the control means effects initiation of fuel delivery by thefuel means at a time which does not precede the opening of the injectorvalve.
 4. A fuel/air injector as set forth in claim 3 wherein theduration of duel injection is increased as the load of the engineincreases during the one running condition of the engine.
 5. A fuel/airinjector as set forth in claim 1 further including further fuel supplymeans for supplying additional fuel to the engine as the load of theengine increases during the one running condition.
 6. A fuel/airinjector as set forth in claim 1 wherein the fuel/air injector unitdelivers fuel directly to the combustion chamber of the engine.
 7. Afuel/air injector as set forth in claim 6 wherein the duration of fuelinjection is increased as the load of the engine increases during theone running condition of the engine.
 8. A fuel/air injector as set forthin claim 6 wherein there is a second running condition of the enginewherein the control means effects initiation of fuel delivery by thefuel means at a time which does not precede the opening of the injectorvalve.
 9. A fuel/air injector as set forth in claim 8 wherein theduration of fuel injection is increased as the load of the engineincreases during the one running condition of the engine.
 10. A fuel/airinjector as set forth in claim 6 wherein the engine is two-cyclecrankcase compression engine and has scavenge port means for deliveringa charge to the combustion chamber from a crankcase chamber and exhaustport means for discharging a burnt charge from the combustion chamber tothe atmosphere.
 11. A fuel/air injector as set forth in claim 10 whereinthe duration of fuel injection is increased as the load of the engineincreases during the one running condition of the engine.
 12. A fuel/airinjector as set forth in claim 10 wherein there is a second runningcondition of the engine wherein the control means effects initiation offuel delivery by the fuel means at a time which does not precede theopening of the injector valve.
 13. A fuel/air injector as set forth inclaim 12 wherein the duration of fuel injection is increased as the loadof the engine increases during the one running condition of the engine.14. A fuel/air injector as set forth in claim 10 wherein the timing ofthe opening of the injector valve is after the timing at which thescavenge port is opened.
 15. A fuel/air injector as set forth in claim14 wherein the duration of fuel injection is increased as the load ofthe engine increases during the one running condition of the engine. 16.A fuel air injector as set forth in claim 14 wherein there is a secondrunning condition of the engine wherein the control means effectsinitiation of fuel delivery by the fuel means at a time which does notprecede the opening of the injector valve.
 17. A fuel/air injector asset forth in claim 16 wherein the duration of fuel injection isincreased as the load of the engine increases during the one runningcondition of the engine.
 18. A fuel/air injector as set forth in claim 1wherein less fuel is injected by the fuel means before the injectorvalve is opened than after the injector valve is opened during the onerunning condition.
 19. A method of operating a fuel/air injector unitcomprising an outer housing assembly defining chamber means, air meansfor supplying air under pressure to said chamber means, fuel means forsupplying fuel to said chamber means, an injector port communicatingsaid chamber means with an engine chamber, an injector valve for openingand closing said injector port, sensor means for sensing engine runningconditions, said method comprising the steps of varying at least theopening of said injector valve at certain sensed engine conditions,holding the time of opening of said injector valve constant in at leasta range of sensed conditions, varying at least the initiation of fueldelivery by said fuel means at certain sensed running conditions, andinitiating the fuel delivery of said fuel means beginning at a timebefore said injector valve is opened and terminating at a time aftersaid injector valve is opened under at least one running condition ofsaid engine.
 20. A method of operating a fuel air injector as set forthin claim 19 wherein the duration of fuel injection is increased as theload of the engine increases during the one running condition of theengine.
 21. A method of operating a fuel/air injector as set forth inclaim 19 wherein there is a second running condition of the engine andinitiation of fuel delivery by the fuel means is begun at a time whichdoes not precede the opening of the injector valve during the secondrunning condition.
 22. A method of operating a fuel/air injector as setforth in claim 21 wherein the duration of fuel injection is increased asthe load of the engine increases during the one running condition of theengine.
 23. A method of operating a fuel/air injector as set forth inclaim 19 further including the step of supplying additional fuel to theengine as the load of the engine increases during the one runningcondition by a source other than the fuel/air injector.
 24. A method ofoperating a fuel/air injector as set forth in claim 19 wherein thefuel/air injector unit delivers fuel directly to the combustion chamberof the engine.
 25. A method of operating a fuel/air injector as setforth in claim 24 wherein the duration of fuel injection is increased asthe load of the engine increases during the one running condition of theengine.
 26. A method of operating a fuel/air injector as set forth inclaim 24 wherein there is a second running condition of the engine andinitiation of fuel delivery by the fuel means is begun at a time whichdoes not precede the opening of the injector valve during the secondrunning condition.
 27. A method of operating a fuel/air injector as setforth in claim 26 wherein the duration of fuel injection is increased asthe load of the engine increases during the one running condition of theengine.
 28. A method of operating a fuel/air injector as set forth inclaim 19 wherein the engine is two-cycle crankcase compression engineand has scavenge port means for delivering a charge to the combustionchamber from a crankcase chamber and exhaust port means for discharginga burnt charge from the combustion chamber to the atmosphere.
 29. Amethod of operating a fuel/air injector as set forth in claim 28 whereinthe duration of fuel injection is increased as the load of the engineincreases during the one running condition of the engine.
 30. A methodof operating a fuel/air injector as set forth in claim 29 wherein thetiming of opening of the injector valve is held constant after thetiming of the delivery of fuel from the fuel means is advanced.
 31. Amethod of operating a fuel/air injector as set forth in claim 28 whereinthere is a second running condition of the engine and initiation of fueldelivery by the fuel means begins at a time which does not precede theopening of the injector valve during the second running condition.
 32. Amethod of operating a fuel/air injector as set forth in claim 31 whereinthe duration of fuel injection is increased as the load of the engineincreases during the one running condition of the engine.
 33. A methodof operating a fuel/air injector as set forth in claim 28 wherein thetiming of the opening of the injector valve is after the timing at whichthe scavenge port is opened.
 34. A method of operating a fuel/airinjector as set forth in claim 33 wherein the duration of fuel injectionis increased as the load of the engine increases during the one runningcondition of the engine.
 35. A method of operating a fuel/air injectoras set forth in claim 33 wherein there is a second running condition ofthe engine and initiation of fuel delivery by the fuel means begins at atime which does not precede the opening of the injector valve during thesecond running condition.
 36. A method of operating a fuel/air injectoras set forth in claim 35 wherein the duration of fuel injection isincreased as the load of the engine increases during the one runningcondition of the engine.
 37. A method of operating a fuel/air injectoras set forth in claim 19 wherein less fuel is injected by the fuel meansbefore the injector valve is opened than after the injector valve isopened during the one running condition.